The present invention relates to a filtration method and filter apparatus for separating suspended solids from a liquid suspension and more particularly, to a filter apparatus constructed to break solids accumulated on the filter media away from the filter media.
The present invention is related to co-pending U.S. Pat. No. 4,622,144 and assigned to the assignee of the present invention.
In accordance with the present invention, it is proposed to provide a liquid suspension filtration apparatus for removing liquid from the suspended solids separated from liquid and deposited on a filter media together with apparatus for removing the solids deposited and caked on the filter media.
This is accomplished generally by introducing a liquid suspension into a pressure vessel having a filter wall section on which the solids are deposited. The vessel is filled so that the entire surface area of the filter section is covered. As the liquid flows through the filter wall section, the suspended solid is deposited and accumulated thereon with the filtrate passing therethrough. When the solids accumulated on the filter section are of such a thickness that further filtration is no longer feasible, flow of liquid into the vessel is discontinued and pneumatic pressure means are actuated to create a pneumatic pressure within the vessel. This causes further flow of liquid through the accumulated solids on the filter section and gradually displaces the liquid suspension from the filter section to expose increasing areas of accumulated solid to the pneumatic pressure. The pneumatic pressure acting on the exposed solids is operative to compress or squeeze the solids against the filter section and remove additional liquid therefrom to form a layer in the nature of a cake. When the excess liquid is displaced from the filter section, the remaining liquid suspension is removed from the vessel and the pneumatic pressure is released. A conduit device is provided between the filter section and the cake build up. In certain filtering applications, it is desirable to provide a fabric filter media over the filter screen section. In such cases, the conduit is placed between the filter media and the screen. The conduit is most typically wound to form a helical pattern around the filter section, and is held at various points throughout its length to the filter screen. When expanded by air pressure, the conduit changes configuration and forms chords between its connection points and thereby causes the expansion of the cake away from the screen. The cake falls through an outlet at the bottom of the vessel.
The above described arrangement is suitable for the extraction of liquids from suspended solids which are substantially air impervious when separated and deposited on the filter section. However, should the separated suspended solid not have the impervious characteristic, the arrangement of the present invention may be provided with a flexible fluid impervious curtain which overlies the filter section. The curtain is constructed and arranged so as to be spaced from the filter section to permit the passage of liquid through the latter. Upon the application of the pneumatic pressure to gradually displace the liquid from the filter section, the flexible curtain is forced into face to face engagement with the solids accumulated on the filter section by the pneumatic pressure acting thereon to compress the solids and extract liquid therefrom in substantially the same manner as described above.